RFR: 8326831 Clarify test harness control variables in make help

[Ludvig Janiuk]

On Tue, 27 Feb 2024 13:55:53 GMT, Ludvig Janiuk <lujaniuk at openjdk.org> wrote:

> Clarifying text in `make help` output on how to list variables for e.g. JTREG='...'.

I'll note that you still need to run configure to execute `make test-only JTREG=help`. Should this really be necessary?

Also, while `make test-only JTREG=help` lists the valid options, it still does nothing to document their meaning.

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PR Comment: https://git.openjdk.org/jdk/pull/18028#issuecomment-1966607480
PR Comment: https://git.openjdk.org/jdk/pull/18028#issuecomment-1966609174